(NaturalNews) Just about week after the Obama administration was finally able to generate some positive news regarding the president's signature legislative achievement, Obamacare, the head mistress in charge of the law's disastrous roll-out has resigned from her embattled post.

News that Department of Health and Human Services chief Kathleen Sebelius - or "Auntie K" as she is known on Capitol Hill, would step down broke on April 10, just two days before President Obama was to make the formal announcement and, at the same time, nominate a political operative, Sylvia Burwell, head of the Office of Management and Budget and the woman who ordered last fall's government shutdown, to replace Sebelius. The Senate will have to confirm Burwell since she's being nominated to a Cabinet post.

The announcement, which reportedly took lawmakers, aides and others in the nation's capital by surprise, comes just days after Obama took a victory lap of sorts in touting 7.5 million enrollees for health coverage under the law. The Congressional Budget Office had announced earlier that at least 7 million enrollees would be needed to ensure that the law would not become a drain on the Treasury.

'Oversaw a disastrous roll-out

Nevertheless, the massive technical difficulties associated with the launch of Obamacare last October, coupled with ongoing concerns about how the law was actually being implemented (or, in many cases, not implemented), hung over Sebelius.

She also leaves ahead of a tough midterm election cycle that is expected to focus heavily on Obamacare's increasing unpopularity.

In the wake of news that Sebelius was stepping down, Republicans nevertheless insisted their criticism of the law would not abate.

"Secretary Sebelius oversaw a disastrous rollout of Obamacare, but anyone can see that there are more problems on the way," Republican National Committee Chairman Reince Priebus said. "The next HHS Secretary will inherit a mess -- Americans facing rising costs, families losing their doctors, and an economy weighed down by intrusive regulations. No matter who is in charge of HHS, Obamacare will continue to be a disaster and will continue to hurt hardworking Americans."

Senate Finance Committee Ranking Member Orrin Hatch added that Sebelius "had one of the toughest jobs in Washington" because she had to implement the law, which he said is "flawed" and continues to fall short.

"While we haven't always agreed, Secretary Sebelius did the best she could during the tumultuous and volatile rollout of the law," Hatch, R-Utah, said in a statement.

Democratic leaders, however, were quick to praise Sebelius, a former governor of Kansas. House Minority Leader Nancy Pelosi of California said Sebelius displayed leadership during the rollout, adding she had "been forceful, effective and essential."

"Her legacy will be found in the 7.5 million Americans signed up on the marketplaces so far, the 3.1 million people covered on their parents' plans, and the millions more gaining coverage through the expansion of Medicaid," Pelosi said.

'Confident in the trajectory'

The White House official said Sebelius notified Obama of her decision to leave in early March, Fox News reported.

"At that time, Secretary Sebelius told the president that she felt confident in the trajectory for enrollment and implementation of the Affordable Care Act, and that she believed that once open enrollment ended it would be the right time to transition the department to new leadership," the official said, adding the president "is deeply grateful for her service."

Sebelius was among the longest-serving Cabinet members of the Obama administration. However, her relationship with the White House had diminished since the bungled Obamacare rollout of glitch-prone online insurance exchanges, which are vital to the law's functioning. Obama and other White House officials complained that they did not get timely information from HHS regarding the lack of progress on the federal exchange especially.

The White House sent management expert Jeffrey Zients to oversee a rescue operation that turned things around by the end of November, Fox News reported.